Groundwater Hydrology, Aquifers, and Site Evaluation
What this domain tests
This domain tests basic aquifer hydraulics and the site factors that affect well performance and protection. Expect questions on porosity, specific yield, storativity, transmissivity, drawdown, recharge and discharge, Nevada hydrographic areas, and setback evaluation.
Core rules and concepts
- An unconfined aquifer is bounded by a water table; a confined aquifer is overlain by a low-permeability layer and stores water mainly by compaction and expansion.
- Porosity is the fraction of void space. Specific yield is the drainable fraction; it is smaller than porosity. Storativity in a confined aquifer is much smaller than specific yield in an unconfined aquifer.
- Transmissivity describes how much water an aquifer transmits; it is hydraulic conductivity times saturated thickness. Darcy's law relates flow to conductivity, area, and gradient.
- Pumping creates a cone of depression. Drawdown depends on pumping rate, aquifer properties, and nearby wells. Specific capacity is yield divided by drawdown and is a useful screening tool.
- Nevada manages groundwater by hydrographic areas. Perennial yield is the long-term sustainable annual withdrawal, not the volume in storage.
- Site evaluation considers contamination sources, septic systems, floodplains, slope, access, and the need to seal off poor-quality or shallow water.
Worked example
A pumping test yields 500 gallons per minute with 10 feet of drawdown. Specific capacity is 50 gallons per minute per foot. If the rate were raised to 750 gallons per minute, a rough linear estimate would be 15 feet of drawdown. The estimate is only a screening check because real drawdown is nonlinear and depends on boundaries, interference, and aquifer confinement.
Traps that cost marks
Using porosity as specific yield; applying unconfined specific-yield values to a confined aquifer; relying on one static water-level measurement; and ignoring flood or contamination risk at the site.